Astronomers and geologists have determined that the universe and Earth are billions of years old. This conclusion is not based on just one measurement or one calculation, but on many types of evidence. Here we will describe just two types of evidence for an old Earth and two types of evidence for an old universe; more types can be found under Further Reading. These methods are largely independent of each other, based on separate observations and arguments, yet all point to a history much longer than 10,000 years. As Christians, we believe that God created the world and that the world declares his glory, so we can’t ignore what nature is telling us about its history.

Age of the Earth from seasonal rings and layers

If you’ve ever seen a horizontal slice of a tree trunk, you’ve seen how a tree forms a new growth ring each year. In years of drought, the tree grows less quickly so the ring is narrower; in good growing seasons the ring is thicker. A tree’s age can be found by simply counting its rings. By comparing the pattern of thick and thin rings to weather records, scientists can verify that the method is accurate. This method can even be used on dead trees that fell in a forest long ago. For example, the last 200 rings in the dead tree might match up with 200 rings early in the life of the living tree, so the two trees together can count back many years. In this way, multiple trees can be used to build a master chronology for a forested region. European oak trees have been used to build a 12,000-year chronology.¹

The annual ice layers in glaciers provide a similar method that goes back much further in history. Each year, snowfall varies throughout the seasons and an annual layer is formed. Like the tree rings, this method can be verified by comparison to historical records for weather, as well as to records of volcanic eruptions around the globe that left thin dust layers on the glaciers. Scientists have drilled ice cores deep into glaciers and found ice that is 123,000 years old in Greenland² and 740,000 years old in Antarctica.³ These annual layers go back much farther than the 10,000 years advocated by the young earth creationists. The Earth must be at least 740,000 years old.

How can an old Earth be reconciled with Genesis? See Scripture Interpretation

Age of the Earth and solar system from radiometric dating

In your high school science classroom, you may have seen a large poster of the periodic table hanging on the wall. The periodic table shows the types of atoms that make up the world around us. An element in the periodic table can come in different flavors called isotopes. Some isotopes are unstable, and over time these isotopes “decay” into isotopes of other elements. For example, Potassium-40 is unstable and decays into Argon-40. As time passes, a rock will have more and more Argon-40 and less and less Potassium-40. Radiometric dating is possible because this decay occurs at a known rate, called the “half-life” of the radioactive element. The half-life is the time that it takes for half the radioactive sample to change from one element into the other.

Some isotopes have short half-lives of minutes or years, but Potassium-40 has a half-life of 1.3 billion years. Radiometric dating requires that one understand the initial ratio of the two elements in a given sample by some means. In this case, Argon-40 is a gas that easily bubbles out and escapes when it is produced in molten rock. Once the rock hardens, however, all the Argon-40 is trapped in the sample, giving us an accurate record of how much Potassium-40 has decayed since that time. So, if we find a rock with equal parts Potassium-40 and Argon-40, we know that half the Potassium-40 has decayed into Argon-40, and that the rock hardened 1.3 billion years ago.⁴

It’s hard to find rocks on the surface of the Earth that have not been altered over time. Most old rocks have been eroded by wind and water or submerged by continental plates. The oldest reliably dated rock formation is in Greenland, where several different isotopes were used to find an age of 3.6 billion years.⁵ Scientists also recently dated zircon grains (which resist erosion) in Western Australia to 4.4 billion years old.⁶ To find older rocks that haven’t been eroded, we need to look beyond Earth. Meteorites are rocks from the solar system that have fallen to Earth recently and haven’t suffered much erosion. Their pristine interiors give an age that dates back to their formation at the beginning of the solar system. Nearly all meteorites have the same radiometric age, 4.56 billion years old.⁷ Thus, the solar system, including the Earth, is about 4,560,000,000 years old.

Age of galaxies from the travel time of light

What about the ages of stars and galaxies, and the age of the whole universe? One way to measure these ages is with the travel time of light. Light travels incredibly fast – 300,000 kilometers per second, or 186,000 miles per second. On Earth, the delay due to light travel time is a tiny fraction of a second. But in space, the distances are so vast that the light takes a substantial amount of time to travel to us: 8.3 minutes from the Sun, 4.3 years from the nearest star, and about 8500 years from the center of the Milky Way galaxy. That delay means that we don’t see these objects as they are right now, but as they were when the light left. The universe actually works as a sort of “time machine,” in which we can see into the past simply by looking far away.

The calculation of the light travel time is simple once you know the speed of light and have a measurement of the distance. The speed of light is well known from experiments on Earth, and various astronomical observations confirm that the speed of light has not changed over the history of the universe. But measuring distances in astronomy is not trivial – you can’t just string a measuring tape from here to the center of the galaxy! Instead, astronomers use several interlocking methods to determine the distances, such as geometric calculations and brightness measurements. For example, some galaxies look much smaller and fainter than other galaxies of the same kind, showing they are much further away.⁸

The Andromeda galaxy, a near neighbor to our own Milky Way galaxy, is 2.3 million light years away. That is, we are seeing it as it was 2.3 million years ago. But that is just our local neighborhood. In recent decades, astronomers have detected galaxies located several billion light years away. If the light has been traveling billions of years to reach us, then the universe must be at least that old. This is completely independent of radiometric dating of the solar system, but both methods point to an age of billions of years, not thousands.

See Did God create everything recently but make it appear old?

Age of the universe from expansion

Not only can astronomers measure the distance of galaxies, they can measure how galaxies are moving. Galaxies are not holding still in space, nor are they moving randomly. Some galaxies are moving towards their neighbors, attracted by their mutual gravity. But the biggest pattern we see is that galaxies are moving apart from one another. This motion apart is not all at the same speed; instead it follows a pattern where galaxies that are further apart are moving more quickly.

This particular pattern indicates the whole universe is expanding. To see why, consider a loaf of raisin bread. The raisins are like galaxies and the dough is like the fabric of space in the universe. As the dough rises, it carries the raisins along, pulling them apart from each other. Raisins that started out on opposite sides of the loaf will be a few inches farther apart after the dough rises, while raisins that started out near each other may only move half an inch. So, the speed of their motion is proportional to the separation between them. In the same way, the space of the universe pulls galaxies further apart as the universe expands.

Astronomers detect a galaxy’s motion by looking at its light spectrum. When a galaxy is carried away by the expansion of space, its light waves are stretched out, making it appear redder. The change in the galaxy’s color is called the red shift, and can be used to calculate its velocity. From the measurements of many galaxies, astronomers can accurately measure the expansion rate of the universe as a whole.

The age of universe can be determined by imaging what the universe looked like in the past, “rewinding” the expansion. In the past the galaxies must have been closer together, and in the distant past they would have been packed together in a tiny point. If we assume that the expansion rate is constant over time, the age for the universe as a whole is about 10 billion years. However, astronomers have been working over the last 20 years to determine how the expansion rate changes with time. We now know that early in the universe the expansion was slowing down, but now it is speeding up. Using careful measurements of this change in expansion rate, the age of the universe is now known quite precisely to be 13.7±0.13 billion years. ⁹

Conclusion

Many different and complementary scientific measurements have established with near certainty that the universe and the Earth are billions of years old. Layers in glaciers show a history much longer than 10,000 years, and radiometric dating places the formation of the Earth at 4.5 billion years. Light from galaxies is reaching us billions of years after it left, and the expansion rate of the universe dates its age to 13.7 billion years. These are just a sampling of the types of evidence for the great age of the Earth and the universe; see the resources below for more.

"The more I examine the universe, and the details of its architecture, the more evidence I find that the Universe in some sense must have known we were coming." — Freeman Dyson¹

"A bottom-up approach to cosmology either requires one to postulate an initial state of the Universe that is carefully fine-tuned — as if prescribed by an outside agency — or it requires one to invoke the notion of eternal inflation, a mighty speculative notion to the generation of many different Universes, which prevents one from predicting what a typical observer would see." — Stephen Hawking and Thomas Hertog²

Fine-Tuning and Pointers to God

Fine-tuning refers to the surprising precision of nature’s physical constants and the beginning state of the universe. Both of these features converge as potential pointers to a Creator. To explain the present state of the universe, scientific theories require that the physical constants of nature — like the strength of gravity — and the beginning state of the Universe — like its density — have extremely precise values. The slightest variation from their actual values results in an early universe that never becomes capable of hosting life. For this reason, the universe seems finely-tuned for life. This observation is referred to as the anthropic principle, a term whose definition has taken many variations over the years.³ 

Constants of Nature

The fine-tuning of the universe is seen most clearly in the values of the constants of nature. There are many such constants, the best known of which specify the strength of the four forces of nature: the strong nuclear force, the weak nuclear force, the electromagnetic force, and gravity. If these forces took on even slightly different strengths, the consequences for life would be devastating.⁴ Two of these in particular, the strong and electromagnetic forces, are responsible for the unusually efficient production of carbon, the element upon which all known life is based. The forces cooperate in such a way as to create a coincidental match up of energy levels, which enables the production of carbon from the fusing of three helium atoms. For three helium atoms to collide and create carbon is very unlikely, however, because under normal circumstances, the energies would not match up perfectly, and the three helium atoms would come apart before they had time to fuse into carbon. It takes a little extra time to deal with the energy mismatch. But, if there is a statistically unusual match of the energies, then the process is much faster. The slightest change to either the strong or electromagnetic forces would alter the energy levels, resulting in greatly reduced production of carbon and an ultimately uninhabitable universe. In the 1950s, Cambridge University astronomer Fred Hoyle recognized the precision of the energy match up, called carbon resonance, and made the following observation:

"A commonsense interpretation of the facts suggests that a super-intellect has monkeyed with physics, as well as with chemistry and biology, and that there are no blind forces worth speaking about in nature. The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question." ⁵

Hoyle did not mean to argue in favor of divine intervention as an answer. The scientific explanation of carbon’s development was readily accessible, although this explanation offers no insight into why the fundamental forces cooperated to produce the unusual energy match up. Hoyle’s remark should be understood as an acknowledgement of how startling it is that the universe has the exact properties that enable the existence of life.

Consider also the strength of gravity. When the Big Bang occurred billions of years ago, the matter in the universe was randomly distributed. There were no stars, planets or galaxies—just atoms floating about in the dark void of space. As the universe expanded outwards from the Big Bang, gravity pulled ever so gently on the atoms, gathering them into clumps that eventually became stars and galaxies. But gravity had to have just the right force—if it was a bit stronger, it would have pulled all the atoms together into one big ball. The Big Bang—and our prospects—would have ended quickly in a Big Crunch. And if gravity was a bit weaker, the expanding universe would have distributed the atoms so widely that they would never have been gathered into stars and galaxies. The strength of gravity has to be exactly for stars to form. But what do we mean by “exactly”? Well, it turns out that if we change gravity by even a tiny fraction of a percent—enough so that you would be, say, one billionth of a gram heavier or lighter—the universe becomes so different that there are no stars, galaxies, or planets. And without planets, there would be no life. The other constants of nature possess this same feature. Change any of them, and the universe, like Robert Frost’s traveler, moves along a very different path. And remarkably, every one of these different paths leads to a universe without life in it. Our universe is friendly to life, but only because the past fifteen billion years have unfolded in a particular way that led to a habitable planet with liquid water and rich chemistry.

There are many other finely-tuned constants of nature besides the strengths of these forces. Consider the ratio of masses for protons and electrons, as a final example. The mass of a proton is roughly 1836.1526 times the mass of the electron.⁶ Were this ratio changed by any significant degree, the stability of many common chemicals would be compromised. In the end, this would prevent the formation of such molecules as DNA, the building blocks of life.⁷ But with regard to the development of life on Earth, it is sometimes claimed that natural selection would find a way for life to develop no matter what the circumstances. In this way, nature is sometimes said to tune itself. However, the fine-tuning of carbon is even responsible for nature’s ability to tune itself to any degree. As professor Alister McGrath has pointed out:

"[The entire biological] evolutionary process depends upon the unusual chemistry of carbon, which allows it to bond to itself, as well as other elements, creating highly complex molecules that are stable over prevailing terrestrial temperatures, and are capable of conveying genetic information (especially DNA). […] Whereas it might be argued that nature creates its own fine-tuning, this can only be done if the primordial constituents of the universe are such that an evolutionary process can be initiated. The unique chemistry of carbon is the ultimate foundation of the capacity of nature to tune itself." ⁸

Initial Conditions

Fine-tuning is also evident in the "initial conditions" or the beginning state of the universe. The initial conditions of the universe include such information as the expansion energy of the Big Bang, the overall amount of matter that was present, the ratio of matter to antimatter, the initial rate of the universe’s expansion and even the degree of its entropy.

Consider the expansion rate of the Big Bang. If it was greater, so the early universe expanded faster, the matter in the universe would have become so diffuse that gravity could never have gathered it into stars and galaxies. If it was less, so the early universe expanded more slowly, gravity could have overwhelmed the expansion and pulled all the matter back into a black hole. The expansion rate was just right, so that the universe could have stars in it.

Another interesting example of a finely-tuned initial condition is the critical density of the universe. In order to evolve in a life-sustaining manner, the universe must have maintained an extremely precise overall density. The precision of density must have been so great that a change of one part in 10¹⁵ (i.e. 0.0000000000001%) would have resulted in a collapse, or big crunch, occurring far too early for life to have developed, or there would have been an expansion so rapid that no stars, galaxies or life could have formed.⁹ This degree of precision would be like a blindfolded man choosing a single lucky penny in a pile large enough to pay off the United States’ national debt.

Responses to Fine-Tuning

Needless to say, the preceding examples carry significant implications for understanding the universe. With some thought, it seems that out of an unfathomable number of possibilities, our universe is one of very few which is capable of hosting life. Consequently, many of these observations have been used as pointers to God.

Fine-Tuning vs. Irreducible Complexity

Before continuing the discussion, it is important to distinguish these pointers to God from the biological arguments of irreducible complexity, which have a similar form. Fine-tuning provides examples of how nature is able to produce the current complexity of life, and when one reflects upon the unlikelihood of these examples, it may have the potential to point to a creator. In the case of irreducible complexity, however, the argument is advanced to suggest that nature cannot account for our present state of existence without relying upon direct, miraculous, divine intervention somewhere in the process.¹⁰ While an argument of irreducible complexity would be shattered by a scientific explanation, these pointers to God are much less vulnerable to dismissal on the basis of future scientific explanations. However, pointers to God also draw attention to the splendid precision of nature’s laws towards the evolution of life.

A Lucky Accident

Not surprisingly, fine-tuning arguments unsettle those who embrace the philosophy of naturalism, since a straightforward interpretation of the evidence points in favor of an intelligent creator. Some of the naturalist responses are common and are worth mentioning here. The first amounts to a nonchalant shrugging of the shoulders. Many adherents to philosophical naturalism give a response along the following lines: Because humans exist, the laws of nature clearly must be the ones compatible with life. Otherwise, we simply wouldn’t be here to notice the fact. To argue against this line of reasoning, John Leslie makes the analogy of surviving an execution at a firing squad completely unharmed.¹¹ Here, Leslie argues that the naturalist’s argument above is analogous to saying, "Of course all of the shots missed, otherwise I wouldn’t be here to notice that I’m still alive!” A much more logical approach would be to seek out an explanation for why such an unlikely event occurred. A good scientific explanation satisfies curiosity, whereas this kind of explanation does nothing to offer any resolution.

An Inevitability

From a more scientific standpoint, it is often claimed that the theory of inflation gives an adequate explanation for such precision and balance. The theory of inflation states that in the early stages of cosmological evolution, the universe underwent a period of exponential expansion. By proposing the right kinds of inflationary models, it is possible to show that some of the examples above — most importantly the critical density of the universe — would naturally take on the appropriate values. In this way, some of the universe’s fine-tuning seems to be explained away. Whether inflation occurs is a subject of debate. However, most theoretical physicists agree that some form of inflation took place, and more importantly this phenomenon could indeed explain many examples of fine-tuning. But what is not always included in the description of these inflation theories, is the extra fine-tuning the theories themselves require. In order to produce such an enormous inflationary rate of expansion — and to result in the necessary values for our universe’s critical density — inflation theories rely upon two or more parameters to take on particularly precise values. So precise are these values that the problem of fine-tuning remains and is only pushed one step back. A second naturalist response is to suppose that the finely-tuned features of our world will someday show themselves to have been inevitable. That is, with an increase in our understanding of physics, it is possible that one day we will discover a Theory of Everything through which all other facts of physics could be explained. Such a theory might even explain why the universal constants and physical laws have to have such specific values. However, each of the finely-tuned features of our world put certain restrictions on the possibilities for the possible Theory of Everything. In the end, only a few specific theories would suffice, and this essentially results in a fine-tuning problem even for Theories of Everything.¹²

The Multiverse

There is a final response, known as the multiverse hypothesis. The multiverse hypothesis claims that there are many other universes in addition to our own. Each of these has different properties, and different values of the basic constants of physics. If the number of these universes is extremely large, it would be less surprising that one of them would happen to provide the specific conditions for life. At first glance, the proposition of many other universes sounds impressively scientific. However, one must keep in mind that the likelihood of ever being able to observe evidence of another universe is extremely remote, since it is unlikely that information could ever pass from one universe to another. Furthermore, there is no guarantee that the process which produces all of these universes would randomly set all the physical parameters in such a way that every possibility is realized. It could be that there are constraints on the characteristics of these many universes and that the production process itself would have to be fine-tuned in some way to guarantee that we get enough variety of universes to account for our remarkable cosmic home. Additional problems arise with the details of proposing a multiverse, which are enumerated in the suggested readings below.